1. Field of the Invention
The present invention relates to an electroluminescent (EL) device, and, more particularly, to an improved EL device with a more secure patterning of fine electrodes, and a method of manufacturing the same.
2. Description of the Related Art
EL devices are self-emission type display devices, and much attention has recently been paid to the EL devices because they have advantageous features suitable for next generation devices, such as a wide viewing angle, a high contrast ratio, and a high response speed. EL devices are classified into inorganic EL devices and organic EL devices, according to the materials used for forming the light-emitting layers.
In particular, studies of organic EL devices have been extensively conducted because of their advantages, including good characteristics in terms of brightness and response speed, color displaying, and so on.
An EL device is basically configured such that an anode is formed on a transparent insulating substrate, e.g., a glass substrate, in a predetermined pattern, a light-emitting layer, consisting of organic or inorganic layers, is formed on the anode, and a cathode having a predetermined pattern is then stacked thereon so as to be orthogonal with the anode.
The organic or inorganic layers have at least a layered structure of a hole transport layer and a light-emitting layer sequentially stacked. As described above, the light-emitting layer is made of either an organic or inorganic material.
Usable materials of the organic layer include copper phthalocyanine (CuPc), N,N′-dinaphthalene-1-yl-N,N′-diphenyl-benzidine (NPB), and tris-8-hydroxyquinoline aluminum (Alq3).
In the above-described EL device, when a drive voltage is applied to the anode and the cathode, holes from the anode migrate to the light-emitting layer, and electrons from the cathode migrate to the light-emitting layer. The holes and the electrons are recombined in the light-emitting layer to generate excitons. As the excitons are deactivated to a ground state, fluorescent molecules of the light-emitting layer emit light, thereby forming an image.
As described above, EL devices are classified into organic EL devices and inorganic EL devices according to the materials used for the light-emitting layers. An explanation will now be given by referring to an organic EL device.
FIG. 1 is a partially exploded perspective view of a conventional passive matrix type organic EL device. As shown, the conventional organic EL device includes a transparent substrate 11, an active area 20 for organic electroluminescence (to be briefly referred to as an active area, hereinbelow), a cap 12, an electrode terminal portion 30, and a flexible printed circuit board PCB 13. The active area 20 is formed on the substrate 11, and forms an image. The cap 12 is adhered to the substrate 11 and encapsulates the active area 20. The electrode terminal portion 30 supplies current to the active area 20, and extends outside the cap 12. The flexible PCB 13 is adhered to the electrode terminal portion 30 extending outside the cap 12, and connects circuits (not shown) for driving the active area 20. The electrode terminal portion 30 includes a first electrode terminal 32 and a second electrode terminal 34.
The active area 20 includes first electrodes, organic layers, and second electrodes on the substrate 11. The first electrodes are connected to the first electrode terminal 32, and can be spaced a predetermined interval apart from each other in a striped pattern. The organic layers are deposited on the first electrodes in a predetermined pattern. The second electrodes are formed on the organic layers such that they are insulated from the first electrodes and are electrically connected to the second electrode terminal.
In such an organic EL device, the organic layers formed at the active area 20 are formed of very thin layers, and the first electrodes and the second electrodes face each other with the organic layers interposed therebetween. Thus, the organic layers may be thinned at the edges of the first electrodes formed in a predetermined pattern, and short-circuits between the first electrodes and the second electrodes may be generated thereat. Also, short-circuits between each of the first electrodes may be generated.
In order to prevent short-circuits between the electrodes, a variety of techniques in which inner insulating films are formed between each of first electrodes have been proposed in U.S. Pat. Nos. 6,222,315, 6,297,589, and so on. In particular, each of the inner insulating films disclosed in U.S. Pat. No. 6,222,315 has a thickness which becomes gradually smaller toward each adjacent electrode, thereby preventing short-circuits at edge portions of the first electrodes.
FIG. 2 is a partially enlarged plan view of a portion “A” shown in FIG. 1, in which inner insulating films 26 are formed between each of the first electrodes 22. FIG. 3 is a cross-sectional view of the line I—I shown in FIG. 2.
In the drawings, the first electrodes 22 are generally formed of indium tin oxide (ITO). Each of second electrode terminals 34 includes a first terminal portion 34a and a second terminal portion 34b. The first terminal portion 34a is formed of ITO like the first electrodes 22. The second terminal portion 34b is formed of Cr, and compensates for a voltage drop due to line resistance.
As shown in FIGS. 2 and 3, an organic layer 28 and second electrodes 24 are sequentially formed. The second electrodes 24 are formed up to upper portions of the second electrode terminals 34, of the electrode terminal portions 30, to then be electrically connected to the second electrode terminals 34.
However, the following problems may arise in the connection between the second electrode terminals 34 and the second electrodes 24.
Whereas the first and second terminal portions 34a and 34b forming each of the second electrode terminals 34 have a height of several thousands of angstroms, the height of each of the second electrodes 24 covering the second electrode terminals 34, typically made of aluminum Al, is generally 1000 Å or less. As shown in FIG. 3, since the second electrode terminal 34 is spaced a predetermined distance apart from the active area 20, and no layers other than the second electrodes 24 exist therebetween, a predetermined step is generated between the substrate 11 and the second electrode terminal 34. Thus, it is required that the second electrodes 24 cover the second electrode terminal 34 while overcoming a step of the second electrode terminal 34 at a portion “B” shown in FIG. 3. In practice, however, the second electrodes 24 may be easily cut at the edge of the second electrode terminal 34, as shown in FIG. 4.
As shown in FIG. 4, the first terminal portion 34a and the second terminal portion 34b of the second electrode terminal 34 may be shaped such that the upper portions thereof protrude compared to the lower portions thereof. Thus, the second electrodes 24 may be disconnected at an edge, as indicated by reference symbol S.
In order to prevent the second electrodes from being disconnected at the edges, it is necessary to form the second electrodes more thickly. However, forming the second electrodes more thickly may deteriorate the current characteristics of an organic EL device, and may increase the driving voltage of a panel.
Further, the organic EL device may deteriorate due to electrostatic shock generated at contact portions between the second electrodes and the second electrode terminals.
As an effort to overcome these problems, Japanese Laid-open Patent Publication No. JP2000-235890 has disclosed a method of forming a port with a gently sloping end connected to an interconnect portion. However, both the port and the interconnect portion are as thin as tens to hundreds of micrometers, so that it is difficult to practically form such a thin port with the gently sloping end. Furthermore, although such a port can be manufactured, the resulting port has an undesirable step at its sloping end.